1. Field of the Invention
The present invention relates to a method for producing sputtering target materials which are used for a Ni—W based interlayer in a perpendicular magnetic recording medium.
2. Description of Related Art
In recent years, there have been remarkable progresses in magnetic recording technology, and heightening record densities in magnetic record media is proceeding due to increasing drive capacities. In magnetic record media for longitudinal magnetic recording systems currently used worldwide, however, attempts to realize high record densities result in refined record bits, which require high coercivity to such an extent that recording cannot be conducted with the record bits. In view of this, a perpendicular magnetic recording system is being studied as a means for solving these problems and improving record density.
The perpendicular magnetic recording system is a system in which a magnetization-easy axis is oriented in the direction vertical to a medium surface in the magnetic film of a perpendicular magnetic record medium, and is suitable for high record densities. For perpendicular magnetic recording, a multi-layer recording medium having a soft magnetic layer, an interlayer and a magnetic recording layer with increased recording sensitivity has been developed. A CoCrPt—SiO2 based alloy is generally used for the magnetic recording layer, and a Co—Zr—Nb based alloy or the like is used for the soft magnetic layer. The interlayer described herein is a nonmagnetic layer which is typically provided for the purpose of having fine grain size structure of the crystal grains in the magnetic recording layer and imparting anisotropy to the crystal orientation.
The use of various alloys, such as Ni based alloys, Ta based alloys and Pd based alloys, is proposed for the interlayer. In particular, Ni—W based alloys have been studied in recent years. A casting process is primarily employed to produce Ni—W based alloys. It is said in general that because a sputtering target material produced by powder metallurgy has a very fine microstructure, the thin film deposited by sputtering is excellent in uniformity and low in failure percentage. There is, however, no publicly-known document in regard to the use of powder metallurgy in the process for producing the Ni—W based alloy target. In particular, in cases other than the sputtering target material, there has been known no example where an alloy powder containing 5 at % W or higher is consolidated.
In relation to the Ni-based alloy, there is proposed a technique for consolidating an alloy powder containing a high proportion of Cr and Mo effective in solid-solution strengthening as W. For example, as disclosed in Japanese Patent Laid-Open Publication No. H6-248378, it is proposed that a super-anticorrosion Ni-based alloy is produced by filling a workable capsule with a super-anticorrosion Ni-based alloy atomized powder and consolidating a filled body thus obtained in a consolidation step. The super-anticorrosion Ni-based alloy atomized powder comprises 0.03 wt % or less of C, 0.1 wt % or less of Si, 1.00 wt % or less of Mn, 19 to 24 wt % of Cr, 15 to 21 wt % of Mo, 1 to 5 wt % of W, 0.01 to 0.5 wt % of V, 1 to 5 wt % of Fe, 0.01 to 0.5 wt % of Al, 0.02 to 0.1 wt % of N, both or either of 0.5 wt % or less of Ti and 0.5 wt % or less of Nb, and the balance Ni and unavoidable impurities, and has a chemical composition range of 35 wt %≦Cr+Mo≦45 wt %.